Manufacture of gasoline



Nov. 6, 1945. N. B. HASKELL I MANUFACTURE OF GASOLINE Filed Jan. 15, 1943 Patented Nov. 6, v1945 i MANcrAcTUnE or GASQLDIE f l Nelson B. Haskell, Port Arthur, '1 ex.ja;s wsignor to The Texas Company, NewA `York, N. Y., a corporation of Delaware Application January 15, 1943, seifiai No, 472,432

` (criss-s) 7 Claims.

This` invention relates to the manufacture of gasoline, hydrocarbons of high antiknock, value from iight or normally gaseous hydrocarbons. More particularly, the invention relates tp the stabilization and fractionation of light or normal# 1y gaseous. hydrocarbon mixtures, and to the re-i covery of desired fractions from refinery gases, to provide suitable charges for further processing in the manufacture of the gasoline hydrocarbons.

One Of the. principal objects of the invention is conserve as much as possible` i the available ist# butano and lishterbuiylenessuch as isolanti?? portion `of propaneinthe recovered fraction to provide afnovel method of stabilizing and i,

fractionating light or normally gaseous hydrocarbon mixtures to effect an improved separation of desired fractions from undesired lighter and heavier hydrocarbons therein.A

Another object of the invention is to provide Yan improved method of recovering from refinery gases, Such as relief gases from a cracking operabsorption oil containing such absorbed hydrof carbon mixtures, to enable the recovery of C4 or C4 and heavier fractions which are substantially denuded of C3 and lighter, while at the Sametime minimizing loss of desirable C4 hydrocarbons.

Another object of the invention is to provide apparatus for carrying'out the above methods, which apparatus is simple in construction, readily controlled, and economical in operation and maintenance.

Other objects and advantages of the invention will be apparent from the following description when taken in conjunction with the accompanying drawing and appended claims. y

It is conventional refinery-practice to recover condensableV light or normally gaseous hydrocarbons, which are present lin ofi-gases'from vari--A ous refinery operations such as cracking, by absorption of these gases in an vabsorption oil, fol# lowed by stripping of the absorbed hydrocarbons ,l Y

charged to the alkylationf unit- This propane iS undesirable as constituting a diluent which raises the pressure required to maintain the charge in liquid phase, and necessitating `the use of expensive and complicated: 'alkylate `fractional@ing equipment to prevent build-.un of propane in the system while conserving isobutane for recycling to the alkylation unit, Where the preliminary fractionation is carriedout under conditions t0 more i completely climi.nateV propane from ,the charge, a substantial loss of isobutane .and butylenes has resulted with :the heretofore known processing and equipment.`

In accordance `with the present inveutioman improved method and apparatus are provided whereby e more complete separation of undesired hydrocarbons, such as propane, is made fromythe desired traction` which Vis subjected to further processing forthe `manufacture of gasoline hydrocarbons. As applied to the recovery of hydrocarbone from refinery gases, this is accomplished by absorbing the gases in a conventional absorption oil, then prestabilizing the rich absorption oil `to remove undesired lighter hydrocarbons,

' such as C3 `and lighter, stripping the resultant than the lighter hydrocarbons removed in the from the absorption oil; The resulting stripped l gases arethen further fractionated to separate fractions thereof, such as a G4 fraction or C3-C4 fraction, for further processingas by alkylation,

polymerization etc. to produce gasoline hydrocaru butane andthe butylenes. In' an endeavor to prestabilizing step and is substantially `denuded of such lighter hydrocarbons. Preferably, this stream of injected hydrocarbons is obtained by recycling overhead condensate from the stripper.

As applied to the recoveryof a C4 fraction for alkylation, the rich absorption oil is first presta- -bilized preferably under high pressure to remove upper portion thereof to serve as reflux; and the recycled condensate from the stripper is introduced into the prestabilizer below the point of introduction of the reflux condensate thereto. The recycled condensate may be mixed in whole or in part with the stream of rich absorption oil for introduction into the prestabilizer; or the recycled,'condensate may be introduced in whole or in part at one or more points of the prestabilizer above or below the point of introduction o f the rich absorption oil. The relative points of entry of the rich absorption oil feed and the recycle condensate into the prestabilizer tower for best operation depend uponthe'average volatilities of the recycle stream and the absorbed hydrocarbons of the rich oil stream, with the stream having the higher average volatility being introduced above the other stream. The point of entry of the rich oil stream can be varied with f advantage in accordance with the character of the equipment and the composition of the feed, as will be obvious to thoseskilled in the operation of stabilizer equipment. VA preferred embodiment ofthe invention is illustrated in the attached drawing, in which the single figure is a diagrammatic illustration of apparatus suitable'for carrying out the method herein described. y 1 Y Referring to the drawing, a wet refinery gas is introduced by line I into absorption tower II where it passes upwardly countercurrent to descending absorption oil introduced into the upper portion of the tower by thelean oil line I2. Un-

absorbed dry gas is removed from the top of the tower by gas line I3 and passes to suitable gas accumulating lines for use as fuel or for other disposition. 'Ihe absorption oil containing the absorbed hydrocarbons, including C1-C5 and a small amount of heavier hydrocarbons, .is discharged from the base of tower II by line I4. This rich oilis forced by pump I5 through a suitable furnace heating coil I6 and thence introduced by line I'I into an intermediate portion of a recycle line 43 back to the prestabilizer I8.

ing the charges to the stabilizer and stripper respectively, it is to be understood that the towers may each be equipped with a gas-fired reboiler or other appropriate heating coil, which can be used in conjunction with the charge heating coil or in substitution therefor. Lean oil is discharged fromthebase of stripper by line 33 and. forced by pump 34 to line I2 for return t o the absorption tower II.

The overhead from stripper 30 passes through line 3l to condensery 36 and thence by run-down line 3'I to accumulator 38, from which condensate is withdrawn by line 39. A portion of the condensate passesby line to pump 4I which forces the latter in part through line 42 to the top of tower 30 to serve as reflux therein, and in part by As shown, this recycled condensate can be introduced into line I'I and mixed with the preheated rich absorption oil for introduction into the tower; or it can be introduced directly into the tower I8 through one or more of branch lines 44, 45, and 46 at a point or points above or below, or bothv above and below the point of introduction of the rich oil to the tower. Again, a portion of the recycle condensate can be addedy to line I'I, and another portion introduced through one of more of branch lines 44, 45, and 46. It is to be understood that the recycle condensate can be introprestabilizer tower I8. This tower may be operated at about Z50-350 pounds per square inch gauge, with a heater outlet temperature of about o-550 F., a bottom tower temperature of about S-450 F., and a top tower temperature of about 10G-140" F., to remove overhead Cs and lighter by line I9. The overhead material is passed through a condenser 2B and thence by run-down line-2| to an accumulator 22, from which uncondensed Ygas is removed by relief line 23; Condensate is withdrawn from accumulator 22 by line 24 and forced in whole or part .by pump 25 through line 26` to the top of prestabilizer I8 to serve as reflux therein. z

A stream of. depropanized rich oil is withdrawn .from the`base oftower I8 by line 28anlpassed Athrough a .heatingcoil 32 and pressure reducing valve 29 intoan intermediate portionof a stripper 30. The pressure isjthereby reduced to about 40-100 pounds per square inch gauge; and this duced into the prestabilizer at other points below the point of introduction of reflux from line 26.

Another portion of the condensate withdrawn from accumulator 38 by line 39 is passed by branch line 41 to pump 48 which forces the condensate to a fractionating tower or charge debutanizer 50. This tower is equipped with a suitable reboiler or heating coil 5I and may be operated ata pressure of 50-100 pounds per square inch gauge with a bottom temperature of about 18o-280 F. and a top temperature of about 125- 175 F. to remove overhead by line 52 a desired C4 cut, and thereby separate the same from Cs and heavier which is withdrawn as bottoms by line 53. The overhead is passed through condenser 54 and run-down line 55 to accumulator 56, from which condensate is withdrawn by line 51. YThe condensate is forced by pump 58 in part through line 59 to the 'top of tower 59 to serve as reflux-therein, and in .part through branch line BIL-which may lead to a suitable conversion unit, such as an alkylation unit, where the C4 hydrocarbons are reacted and converted into gasoline y hydrocarbons of high antiknock value.

tower 3l] may be operated with a bottom temper- `ature ofV about #15G-500 F. and a top temperature of about 125-1'75 F. to strip out and remove overhead through line 3i remaining absorbed hydrocarbons including C4, C5, and any heavier. It is tobe understood that the above mentioned figures ,for pressure and temperature of the prestabilizer vand-stripper are given merely by way of example;

and these figures can be altered substantially dependingupon the particular charge and vconditions of operation employed. While ,gas-fired heating coils I 6 and 32 have been shown for heat- In continuous operation, there will be a buildup ofthe Ci-Cs stripper condensate in the system to provide the necessary quantity for recycling through line 43, as well as to supply the requirements for stripper reux throughline. 42, and eventually furnish sufficient charge passing through line 49`V for further processing. The 'proportion of condensate recycled onV the basis of the feed of rich oil to the prestabilizer4 can be varied within wide limits. Even ka small proportion of recycle effects improved results as'shown by a decrease in the propane content of the condensate. Ordinarily, the ratio by volume'of recycled condensate to rich oil feed may vary between l part of recycle to parts of rich oil feed up to about 1 part of recycle to IOpartsfofvrich oil feed; and preferably Va ratio of around l part of recycle to around 2Q parts of rich 'oil feed is employed.

, While the use of the stripper condensate as the K hydrocarbonstream which is injected into the prestabilizer providesa-preferred operation, it is to be understood that any available C4 stream from faniextraneous source can be em'pknred.4 :As shown, Van available `refinery C4 strearngsuch as froml the stabilization of f cracked naphthag" or natural gasoline, or from the stabilization' and fractionation of gasolines produced by catalytic conversion, or from A compressing cracking4 still gases, is introduced by pump 62 through line-63, which latter communicates with iine I3. Y Arportion of the injected hydrocarbon streammay be obtained -by vrecycling stripper condensate, and another-portion obtained from an external source -By Way of example, the following table sets forth data obtained in full scale plantgoperationoi an absorption*prestabilizingf and 'stripper assembly of f the character described above, in therecovery from wet refinery gas and the preparation of `a C4 charge for a' catalytic alkylation unit. While one absorption tower Il has been'vshown inthe drawi-'ng it willibe'understood that any number lof -absorption `towers can be employed `in parallel or series. In the runs listed below, three absorption towers were used in parallel, 'and' the rich oil fromthe three towers was combined, prestabilized andstripped. The dataset forth intheiofliowing four columnsv was' obtained on four diilerent days of operation of the same plant, utilizing diierent rates of stripperl condensate recycleon the dif-V ferentrespeotive days. Theconditions of opera-v 4tionand the results obtained were as follows:

Table Prestabilizer: y

Tower pressure, lbs/sq. in. gauge. 310 310 310 310 Temeratures, QF.: Y i i harge to tower. 408k i 413 `380 368 Heater 'out1et 533 528 506 506 vTower bottoml 404 i 400'- 369 361 Toweritop llo 111 113 l,111 Accumulator.- 93 98 96 Rates, B. 1 H Y f 'Y Rich oil charge 1,683 1,701 1,701` 11H03 Ref l\1x 444 4 83 483 482 Stripper condensaterecycle .i 30 75 L231 Stripper: t i l, 1

-Tower pressure, lbs/sq. inqgauge.v '70 `69 69 69 Accumulator pressure, lbs/sq. in. i *i gauge -60 48 l 35 133 Temperatures,-F.: Y f Tower bottom. 488 14115;' '468 i 469 Tower top--..- 160 160 163 163 Charge to tower; 529 516 510 510 Accumulator 80 87 80 81 Rates, B. l?. H.:

Lean oil out 1, 535 l, 514 1, 431 1, 396

Stabilized condensate 131 13 129 128 Propane content of stabilized conden- Y sate, per cent 32. 3 18. 8 11.0 8. 9

From the above, it will be noted that increasing the stripper condensate recycle rate from 0 to 81 barrels per hour with the rich oil lfeed rates shown resulted in a decrease in propane content of the stabilized condensate from approximately 32% to 9%. It is indicated that further increase in the ratio of recycle to rich oil feed would further reduce the propane content of the condensate. As the resulting condensate normally constitutes only a portion of the alkylation charge, other substantial portions being obtained from the stabilization of cracked naphtha and from fractionation of natural gasoline to supply additional isobutane, it will be appreciated that this invention enables the propane content of the charge to be reduced in a simple and economical manner to a very low figure while minimizing loss of desirable C4 hydrocarbons.

While the invention has been described above as applied to the stabilization and fractionation of rich absorption oil, it is of course readily evident that the principles-thereof arelappI-ieableto the stabilization and"l fractionation!offlight for normally gaseous hydrocarbon mixtures gener` ally. Moreover, while theinvention has been specifically described Vin yconnection" with the deprepanization and recovery ofa C4 fraction, 'itis to e be understood thatthe invention is also "applica` ble to the recovery Aof i -hydrocarbninA fractions4` of diierent molecular weights. `For example, a-Cs fraction oanbe recoveredV by presta-bilizing to re move C4 and lighter, andrecyclingto the pre; stabilizer a C5 condensate.` Likewise-ja sharp separation betweeniCiand C: maybe effectedby prestabilizing to remove Cz and lighter varid;r e cyclingto the prestabilizer a Ca fraction.

Obviouslymany modifications and variations of the invention, as hereinbefore set for-th, maybe made without departing from thespirit andscope thereof, and therefore only `such Vlimitations should be `imposedffas areind-icated in the append edolaims. l*

1. The lmethod in therecovery of a desi-red Cr fraction from reiinerygasesbontaining C4 hy'`A` drocarbons and both heavier and lighter hydrocarbons than C4, whichcomprises absorbing the refinery gases in alean absorption oil, presta# bilizing the resulting rich absorption` oil toiremove overhead vCi ,and any lighter-hydrocarbons,

condensing a portion ff'said-overhead l-Crfarid any lighter hydrocarbonsand returningat `least a part of the said condensate asreiiuxto-an upper portion of the prestabilizing lzone, stripping the prestabilized rich absorptionoil to remove C4 and substantially all heavier absorbed hydrocar-` bons to therebyrecover a lean absorption oil, re# cycling saidflean absorption oiltothe absorption step, condensing at least a portion ofthe Cir` heavier hydrocarbons removed by stripping,` re-v turning a portion of the `C4 and-heavier Vcondensate to -thelstrlppng'stepto serve asreilux thereimpassing another portion of the Ci and heaviercondensateto a fractionating'zone where the ldesired C4 fraction is separated `from heavier hydrocarbons, removing the desired C4 fraction overhead froinlvsaid fractionating zone and-suba' jecting the. sameto condensation, returning' a portion' VHof the `resulting` `condensate asrefluii to an upper portion of said fractionating zone, discharging the balance of said condensate from the system as the recovered C4 fraction, and injecting into the rich oil prestabilizing zone at an elevation substantially below the point of reflux return thereto a hydrocarbon stream heavier than the C3 and any lighter hydrocarbons removed overhead therefrom, said stream being largely denuded of said C3 and lighter hydrocarbons but containing a substantial proportion'of the desired C4 hydrocarbons, whereby a more complete separation of the undesired C3 and any lighter hydrocarbons from the C4 and heavier hydrocarbons is eiected in the prestabilizing step while minimizing loss of desired C4 hydrocarbons in the prestabilizing .-step,the reiiu;v for-that step` is introduced into an upperportion o f sai il rzowr1e, and y thesaid injected hydrocarbon streamnlisv mined` in part withthe rich absorption oil f orintrodnc-VA tioninto Said zene and n-troducedr'in. part-.1

of introduction o f said rich abSQI'Dtion pil;

rectlyfinto said zone at a point below the'pointf 4. The method according to claim 1, wherein the inieted hydrocarbon ,streameemprees at.

least in part-ca lpcrton of ,theC4 .and heavier:

overhead condensate fromsaidstripping ;s t epj.; v

5. The methodlinitherecoveryof a lC icontain-- l oilrto remove overhead C4 and heavier andrecover a lean absorption .oil which is. recycled` to the absorption step, condensing atleast a portion of said C4 and heavier overhead from the stripping step, fractionatingaportionof said stripper condensate to :separate the desired C4-containing hydrocarbon fraction overheadfrqm heavier hy.- drocarbons removed as bottoms, diverting atleast a portionofsaid last-mentioned overhead from the system as the recovered Cr-containing hydrocarbon ractionandlrecycling ano-ther portion of the said stripperfcondensatefto the prestabilit-` ing step and introducing the same therein at a plurality of different elevationswhich are.. all below the point of-reflux return to said prestabilizing zone.

6. The method inthe recovery of a C4 hydro-r carbon fraction fromreiinery gases containing Cz-Cs hydrocarbons, whichcomprises ysubjecting the refinery gases to treatment -withan absorption oil, prestabilizingthe resulting-rich absorption oil to remove overhead absorbedgCaand lighter subjecting said overhead C3` and lighter to cooling and condensation; returning at least ai'portion of the resulting condensate :asreux t'o .an

termediate portion of a fractionating 4 zoneof the tion of said Cal-Cs condensateto separate a C4 fraction overhead from heavierjhydrocarbons, condensing said-overhead C4 Afraction and dischargingV at leasta portion of said condensate as the recovered C4 l 1ydrolcarbon fraction.

'7. Apparatus of the characterdescribed compr-ising, in combination, an absorber, V.means for supplying hydrocarbon gases and an absorption oil to said absorber, Va prestabilizer, means for supplying` rich absorption oil from said absorber to said prestabilizer, means-forheating said prestabilizer to remove lighter hydrocarbons therefrom including a heating `coil for the hydrocarbon charge supplied thereto, a condenser and accumulator Aconnectedfto the overheadlineof said prestabilizer, a reflux pump and reflux line for returning condensate from said accumulator to an upper portion of said prestabilizer, a stripper, means for supplying prestabilized rich oil from said prestabilizer to said :stripper including a pressure release valve for lowering the pressure on the hydrocarbons insaid stripper, means for supplying heat to said stripper tov remove remaining absorbed hydrocarbons from said rich oil, means for returning lean oil from said' stripper to said absorber, a charge fractionator, means for supplying overhead hydrocarbons from said stripper to said charge fractionatonwand means for recycling a portion of said overhead hydrocarbons from said stripper to said prestabilizer including a condenser for condensing at least a portion of said overhead and an accumulator for the condensate, a pump for supplying condensate at least at the prestabilizer pressure, and a line from said pump opening into said rich absorption oil supplying means between said heating coil and said prestabilizer. i NELSON B. 'HASKELL 

